This issue was originally marked as duplicate of issue 160431, that is already resolved. This issue is still valid, so this seems to be another issue, but it might be related.

Build: NetBeans IDE Dev (Build 090806)
VM: Java HotSpot(TM) Client VM, 14.0-b16, Java(TM) SE Runtime Environment, 1.6.0_14-b08
OS: Windows XP, 5.1, x86

User Comments:
GUEST: i was about to add a function in a class

GUEST: Copy & Past some lines in PHP-Editor

Lopura: clicking on send a error report
(though it might be possible that I switched the two causes, since after clicking on send an error report I had two of theses windows to report a problem, but I didn't know which was the original error and which one was caused by trying to send the error report)

GUEST: Dragged the scrollbar in the edit window of an html file.

GUEST: I was saving my project. (ctrl + s). I accidentally opened Netbeans two times at the same time before the error occurred.

charlweed: Editing c++ class file. Adding public member function.



Stacktrace: 
java.lang.AssertionError: visnodes.size()=12 snapshot.size()=11
        at org.openide.explorer.view.VisualizerChildren.recomputeIndexes(VisualizerChildren.java:87)
        at org.openide.explorer.view.VisualizerChildren.added(VisualizerChildren.java:223)
        at org.openide.explorer.view.VisualizerEvent$Added.run(VisualizerEvent.java:106)
        at org.openide.util.Mutex.readAccess(Mutex.java:362)
        at org.openide.util.Mutex$1R.run(Mutex.java:1301)
        at org.openide.nodes.Children$ProjectManagerDeadlockDetector.execute(Children.java:1811)